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  1. #1
    Join Date
    Nov 2006
    Location
    Bay Area, California
    Posts
    12

    Confused Heat and Cool simultanously - efficiency

    Hi,

    I'm having an HVAC system designed for a commercial building. We have a meeting room, offices and front lobby. The mechanical engineer told me that we cannot use one unit for all areas and zone it since the meeting room can get hot when many people are in, while the lobby can get cold. So a single unit cannot serve both zones. This makes sense, but under this scenario we are going to have cooling on one room and heating on the next room. It sounds terribly inefficient.

    Does anyone has a suggestion for a more efficient method?

    Thanks,

    Grumit

  2. #2
    Join Date
    Dec 2007
    Location
    Southern, CA
    Posts
    520
    Hold the meetings in the lobby? Tough to say without a lot more info, listen to the engineer.

  3. #3
    Join Date
    Mar 2003
    Posts
    7,326
    Not sure of your configuration, but there are at least two systems available that can offer you individual room control, and simultaneous heating/cooling. Daikin is one and Mitsubishi City Multi is the other. Each is a good system, with many features and energy recovery to allow simultaneous heating/cooling. They are extremeyl quiet, and very energy efficient, although for some contractors and engineers, they just don't get it. We have installed a bunch and they work great. There are others here who have had similiar results.

  4. #4
    Join Date
    Nov 2006
    Location
    Bay Area, California
    Posts
    12
    > Hold the meetings in the lobby?
    Can't do that!-)

    I've listened to the engineer. I understand this is the straightforward and conventional way, but I'm not happy since it's not efficient.

    Meeting room is about 400 SF. Lobby and office area is about 2000 SF. Stand alone building.

  5. #5
    Join Date
    Nov 2006
    Location
    Bay Area, California
    Posts
    12
    Thank you flange, I'll suggest these options.

  6. #6
    Join Date
    Sep 2007
    Location
    Yuma, Arizona
    Posts
    252
    It's not uncommon to run Cooling and Heating systems simultaneously. I have a building cooled by a chiller using vavs with reheats in them. While the chiller is running the boilers run pretty much most of the day to warm up cool spots and also help dehumidify. Many large and small buildings operate this way.

  7. #7
    Join Date
    Nov 2003
    Location
    Rochester, New York
    Posts
    392
    Its absolutly possible. VAVS with reheats is all you need. As said before, it will reheat the air dehumidy and it goes along its merry way. This is common practice in well designed office buildings. I would look for a new Engineer if this is all he/she has.

  8. #8
    Join Date
    Dec 2005
    Posts
    107
    Simultaneous heating and cooling violates ASHRAE 90.1.
    Not the most energy efficient concept for the new batch of green buildings.
    But it works real well and makes allot of sense in a building like this.

  9. #9
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,607
    If you are using conventional equipment, split system or rooftop unit, in smaller sizes, a good zone panel will alternate between heating & cooling. Usually they'll do 15-20 minutes of each function then switch to the other.

    Be sure the A/C is set up for cold weather operation or has an economizer.

    Yes, it is inefficient but not unusual for commercial properties.

  10. #10
    Join Date
    Sep 2006
    Location
    Rhode Island
    Posts
    244
    This is not an unusual situation..... I have worked in many buildings that require cooling in one room while at the same time heating in another. Several types of systems can do both at the same time from the same air handler without excessive use of energy.

    Of course I say all of this without knowing what your requirements for the system are. If your requirements are limited then so to will your options be.

  11. #11
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,485

    Air-to-Water Heat Pumps...

    ...closed loop with tower and boiler:

    http://www.mcquayservice.com/mcquayb...gNews/1002.pdf

  12. #12
    Join Date
    Dec 2005
    Posts
    107
    most of these systems will be code violations in 5 years.
    welcome to the world green buildings.
    the costs and maitenance will be huge.
    bright futures await, i hope.

  13. #13
    Join Date
    Sep 2007
    Location
    Yuma, Arizona
    Posts
    252
    nik99, I don't believe that any code violations will take place in 5 years from now on the system that I have described. I'm sure thousands and thousands of buildings use the same approach to manage space temperature and humidity. Maybe I should better explain the design...

    (1) air handler controlling let's say 50 vav's with reheats. Maintain a 55degree discharge air temp by throttling the CHW valve. Eventually your going to overcool a few zones. To fix a cool zone you drive open the HW valve at your reheat in the vav to warm up the zone. This way you can maintain your desired zone temperatures through out the building.

    It's not really wasting energy, what your really doing to keeping people comfortable, just like any other system would be expected to do.

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